Ceramic or composite blank

ABSTRACT

A ceramic or composite blank for the purpose of attaching it to at least one magnet in the clamping chuck of a machine for material-removing processing, supporting a magnetic or magnetizable part on at least one of its two opposite sides.

The fabrication of dental prostheses by means of CAD/CAM (computer-aideddesign/computer-aided manufacturing) processes has increasinglywidespread use. There are a series of processes using computer-aideddesign/computer-aided manufacturing of dental prostheses, e.g. themilling of ceramic blanks according to 3D data sets (EP 904 743, DE 19838 238 A1, DE 101 07 451A1, CEREC® system by Sirona Dental Systems,PROCERA® system from Degussa, LAVA® system manufactured by 3M Espe).Instead of ceramic blanks, millable composite blocks (consisting ofpolymer(s) and inorganic and/or organic fillers) can also be used asblanks.

In these milling processes, usually a rotatable blank is clamped into amachine tool for processing the blank by removing material (EP 160 797B1). For this purpose, the blanks are provided with an integrated holderthat enables the clamping. Such holders are described in e.g. DE 44 36231 A1, WO 0245614, EP 455 854 B1 or EP 982 009 A2. The holders aregenerally discarded after use, thus wasting the ceramic or compositematerials that are relatively expensive and also require complexmanufacturing processes; this results in higher costs.

The process that has now been developed provides a surprisingly simplesolution to this problem.

The invention concerns ceramic or composite blanks with at least onemagnetic or magnetizable part mounted on it sideways. This partcorresponds to the contours of at least one magnet in the clamping chuckof the machine. For the magnetic or magnetizable part and the magnet ofthe clamping chuck usually a flat form fit will suffice. However, thiscan also be a structured fit that provides additional footing.Preferably two opposite recesses are provided on the blank, into whiche.g. an iron part or a steel part is inserted such that it fitsaccurately. The part only needs to be fixed in such a way that it doesnot get lost during use. Once it is clamped, it is retained in itsposition by pressure. For the purpose of clamping, the milling machinehas a magnetic device, usually a plate on which the metal part of theblank is mounted.

FIG. 1 is a sketch of a cylindrical blank 1; wherein the magnetic part 2is arranged in the clamping axis. FIG. 2 illustrates a similar blankwith a structured part 2.

1. Ceramic or composite blank having two opposite sides, said blankcomprising a magnetic or magnetizable part supported on at least one ofsaid two opposite sides.
 2. Blank in accordance with claim 1, whereinthe part is embedded at least partly in the blank.
 3. Blank inaccordance with claim 1, wherein the part is a cylinder or a cuboidblock.
 4. Blank in accordance with claim 1, wherein the part is made ofiron or steel.
 5. Blank in accordance with claim 1, wherein the part isflat on a side facing the clamping chuck.
 6. Blank in accordance withclaim 1, wherein the part is structured on a side facing the clampingchuck.
 7. A method of preparing a dental prosthesis comprising: a)providing a blank in accordance with claim 1; b) mounting the blank bythe magnetic or magnetizable part into a milling machine; and c)processing the blank to form a dental prosthesis.